Summary of Work: Our group is interested in understanding the role of the intersectin adaptor protein in regulating signal transduction cascades. Intersectin is a member of a growing family of adaptor proteins that possess conserved Eps15 homology (EH) domains as well as additional protein recognition motifs. EH-containing proteins play an integral role in regulating clathrin-mediated endocytosis. Intersectin consists of two NH4-terminal Eps homology (EH) domains, a coil-coil region and 5 tandem Src homology 3 (SH3) domains. A variety of experiments have implicated intersectin in the regulation of endocytosis. However, several lines of evidence suggested to us that intersectin might also function in regulation or activation of signal transduction pathways. First, like many cytoskeletal and signal transduction proteins, intersectin contains multiple SH3 domains. Second, in vitro experiments suggested that intersectin?s SH3 domains may interact with the Ras exchange factor, Sos. Third, certain splice variants of intersectin possess an extended carboxy-terminus consisting of a Dbl homology (DH) domain, a pleckstrin homology (PH) domain and a C2 domain suggesting an involvement in the regulation of small GTP binding proteins and Ca+2 homeostasis. And finally, overexpression of Eps15, which physically associates with intersectin, induces oncogenenic transformation. Using transient transcriptional reporter assays, we have shown that intersectin overexpression leads to activation of the Elk-1 transcription factor. Although Elk-1 is a major transcriptional target of the MAPK pathway, we have demonstrated that intersectin activation of Elk-1 is MAPK-independent. In further support of the notion that intersectin activates signaling pathways, we have shown that intersectin expression induces oncogenic transformation of rodent fibroblasts and accelerates progesterone induced maturation of X. laevis oocytes suggesting that intersectin my link endocytosis with regulation of cell growth and differentiation. Our current focus is on understanding the mechanism of intersectin activation of Elk-1 and the importance of this activity for intersectin function. In addition, given its role in regulation of endocytosis, we are currently examining the possible function of intersectin in RTK signaling through regulation of RTK endocytosis, recycling and degradation. - receptor tyrosine kinase, Elk-1, MAPK, signal transduction